Immunity is non-susceptibility that may be either congenital (genetically predetermined) or acquired (developed during the life after natural or artificially induced (immunisation) exposure to particular disease agents).

The immune system allows us to live and survive in this world, by protecting our body from everything that is strange and dangerous (bacteria, viruses, fungi, parasites, stress, radiation, non-systematic use of medications and other factors) and in the event of any extreme conditions.

The objective of the numerous factors of the immune system is to protect the body against any aggression, irrespective of its origin.
Immunity is not characterised by any individual parameter, it is so complicated that knowing the amount of one or another type of immune cell is not enough. If these good cells that protect our body – leukocytes and lymphocytes – start proliferating beyond control, lymph or blood cell cancer may occur.

Usually the immune system of a human can discern between the structures of the body and foreign structures. However, sometimes the settings of the complex mechanism of the immune system break down and the system starts functioning in excess, inappropriately, and causes allergic reactions, instead of protecting. Or it reacts in error and produces antibodies that attack the normal tissue of the body itself.

Autoimmune pathologies are diseases, the pathogenesis of which involves lymphocytes that induce destructive mechanisms by recognising the membranes of the cells of the body itself or native molecules of intercellular substance and initiating immune inflammation. To diagnose an autoimmune pathology, the hormonal or cellular immune reactivity directed against the components of the body of the patient themselves must be proven. Any autoimmune disease is characterised by a long-term, chronic course with periods of remission and aggravation, like in the patients with chronic infectious diseases.